Heart disease is the leading cause of death in the United States. A heart attack, also known as an acute myocardial infarction (AMI), typically results from a blood clot or “thrombus” that obstructs blood flow in one or more coronary arteries. AMI is a common and life-threatening complication of coronary artery disease. Coronary ischemia is caused by an insufficiency of oxygen to the heart muscle. Ischemia is typically provoked by physical activity or other causes of increased heart rate when one or more of the coronary arteries is narrowed by atherosclerosis. AMI, which is typically the result of a completely blocked coronary artery, is the most extreme form of ischemia. Patients will often (but not always) become aware of chest discomfort, known as “angina”, when the heart muscle is experiencing ischemia. Those with coronary atherosclerosis are at higher risk for AMI if the plaque becomes further obstructed by thrombus.
Detection of AMI often involves analyzing changes in a person's ST segment voltage. A common scheme for computing changes in the ST segment involves determining a quantity known as ST deviation for each beat. ST deviation is the value of the electrocardiogram at a point or points during the ST segment relative to the value of the electrocardiogram at some point or points during the PQ segment. Whether or not a particular ST deviation is indicative of AMI depends on a comparison of that ST deviation with a threshold.
Acute myocardial infarction and ischemia may be detected from a patient's electrocardiogram (ECG). An ECG is a highly useful diagnostic aid for clinicians, for the study of heart rate and rhythm. An electrocardiogram is defined to be the heart's electrical signal as sensed through skin surface electrodes that are placed in a position to indicate the heart's electrical activity. The ECG indicates the propagation of low amplitude electrical signals, commonly referred to as the cardiac impulse, across the myocardium giving information about depolarization and repolarization characteristics of the heart.
An ECG typically receives signals from a plurality of electrodes (3, 5, and 12 are common numbers). Historically, the 12-lead surface electrocardiograph has been the most commonly used. A surface ECG refers to placement of electrodes on the surface, or skin, of the patient as opposed to directly to cardiac tissue which obviously requires an invasive procedure. This method attaches about 10 wired electrodes to a patient's body in order to measure the bio-potential activity of the patient and uses the electrodes to transfer the information into the electrocardiogram. The measurement is possible because electric activity surfaces from the cardiac muscle to the skin and dissipates throughout the conductive skin layer. Since the skin has electric impedances, the conductivity of the electric current varies depending on the direction of the measurement and the separation distance of between the measurement electrodes. The ECG monitors voltage signals appearing between various pairs of the electrodes and performs a vector analysis of the resultant signal pairs to prepare various two-dimensional voltage-time graphs indicative of internal cardiac activity.
ECG measurements have been conducted for over 200 years, and a standard configuration of the measurement vector leads have been adopted by the medical and engineering communities. This standard of leads formation and configuration require substantial separation of points of measurements on the surface of the skin, which necessitates connection of two remote points by lead wires into an instrumentation amplifier. This large separation between electrode contact points maximizes the surface area of the skin between the measurement electrode points and therefore maximizes the impedance, and measured voltage potential across the contact electrodes.
The use of the conventional ECG requires large separation between electrodes in order maximize impedance and measure the voltage potential across the contact electrodes. The required separation, leads to large wired footprints on the patient.
If the distance d is too small the bipolar ECG signals will be buried in the noise. If d is increased the signals will increase and in the most extreme variant the measuring electrodes will be positioned as in the EASI system, stretching over the whole torso. However, in the EASI system four unipolar measurements are used to synthesize a standard 12-lead system. In the process of synthesizing ECG from non-standard electrode placement (such as the EASI system and the system disclosed herein) parameters are used to transform the non uniform ECG to standard ECG leads. However, the variance in body impedance between different people is an evident source of error.
Further, the use of a wired monitoring system makes taking a patient's ECG very uncomfortable. Even further, wired devices make patient monitoring very cumbersome for the practitioners and increases the probability of infection due to the exposure of bodily fluid by the wires. To overcome these shortcomings associated with wired monitoring, the use of wireless monitoring devices is being investigated. Wireless monitoring devices will provide increased comfort for a patient, decreased lead-off alarms due to tugged wires, reduced error in lead connection and reduced substantial motion artifacts and RF interference.
Further, providing an epidermal communication network (ECN) where these and other wireless devices can communicate without the need for wired or wireless connectivity can further enhance a user's experience, reduce power consumption and increase data throughput. The ECN is a novel communication means for transmitting and receiving information across the human body. By using the human body as a communication network, seamless integration of smaller, less obstructive, and more naturally integrated wireless sensors across the entire body can be possible.
In U.S. Pat. App. No. 2012/0165633 to Mohammad Khair, partial wireless monitoring was introduced. The ECG measurement system uses wired electrodes only for calibration purposes. In this method, the calibration is started from the ECG receiver unit which sends selection signals and synchronization pulses via its radio module to the radio module of each ECG sensing unit. As a consequence, preselected passive electrodes are connected to each ECG sensing unit, in predetermined sequences, such that the measuring module of each ECG sensing unit generates signals. Following an A/D-conversion and data processing in the data processing unit, local bipolar data for each ECG sensing unit and calculated standard ECG data are stored digitally in a buffer memory in the data processing unit. This digitally stored data representing one and the same heart beat, are then compared in order to determine the parameters of a transfer function by which the standard ECG leads may be synthesized from the local bipolar ECG data. Once these parameters have been determined, the calibration phase can be terminated and the passive electrodes can be detached from the body of the patient and the multi cable connection can be disconnected from the ECG sensing units.
However, this solution is not a complete wireless solution and the use of wired electrodes still makes it very cumbersome to work with. With the current advancements in technology and electronics (i.e. the use of instrumentation amplifiers), the separation required for ECG measurements is decreasing, thus making it easier to find a reliable wireless monitoring device.
In U.S. Pat. No. 5,811,897 to Spaude et al, a device for body-bound data transmission is introduced and incorporated herein in its entirety. The transmission of the data between two terminals in which a portion of the body of a user completes the data transmission circuit is described. A first terminal is worn by a body of a user, and an interface is provided for coupling the data signals into the body and/or for coupling them out of the body. A second terminal with a touch-sensitive interface by way of which, in the case of a contact by the body wearing the first terminal, couples data signals coupled into the body out of the body and/or couples data signals into the body.
However, this solution is not the most efficient. It requires the use of two or more pairs of electrodes on each part of the body terminals. Further, the solution presented by Spaude requires the transmission of signals through the body as high frequencies are referenced. A need for a wireless single electrode solution communicating at low frequencies with low power consumption is needed. Therefore, it is the object of the current embodiment to present a wireless monitoring device with the capability to communicate over an epidermal communication network.